Strength-enhanced, lightweight lignocellulosic composite board materials and methods of their manufacture

Abstract

Lighweight lignocellulosic board materials, such as oriented strand board and others, having reduced densities while maintaining suitable mechanical properties, and methods for their manufacture.

Description

FIELD OF THE INVENTION The present invention relates to lightweight lignocellulosic composite board materials, such as oriented strand board and the like, having reduced densities and sustained mechanical properties like bending strength, and methods of their manufacture. BACKGROUND OF THE INVENTION Oriented strand board (“OSB”) is commercially available. OSB material generally is formed of multiple layers of wood “flakes” or “strands” bonded together by a resin binder under heat and compression to provide a unitary board structure. The flakes are made by cutting logs into thin slices with a knife edge oriented parallel to the length of a debarked log. The cut flakes are broken into narrow strands generally having lengths oriented parallel to the wood grain that are larger than the strand widths. In one common fabrication of oriented strand board, the flakes generally are first dried to remove water, and are then coated in a blender with a thin layer of binder and sizing agent. T...

AI Technical Summary

Benefits of technology

The present invention relates to lightweight lignocellulosic composite board materials having reduced board density while maintaining good structural strength by introduction of a low-density filler comprising hollow or cellular microspheres in the board-forming composition.

In one embodiment of the present invention, a density reduction of at least a 5% reduction is achievable in composite lignocellulosic panels, like oriented strand board, without encountering bending strength reductions, as compared to making the same dimensioned panel with the same composition except without the microspheres.

In one instance, incorporation of the hollow or cellular microsphere filler in OSB plies comprising furnishes of southern pine flakes and strands, and a thermosetting resin, effectively reduces the density of the consolidated panel made with those plies to less than 40 pounds per cubic feet (pcf), where it otherwise would have been 42 or more pcf if made with the same board-forming compositions except omitting the microspheres, and without loss in bending strength.

This invention also encompasses unique methods for making these lignocellulosic composite board materials. In one preferred embodiment, the hollow microspheres are blended with thermosetting resin in sufficient respective amounts that the resin is borne on the exterior surfaces of the microspheres as a surface coating effective to provide a moistened granular material. This moistened granular material is used to provide a resin source as carried upon the microspheres, instead of a resin dispersion of microspheres. The moistened granular material is thereafter conveniently admixed with wood strands in the board making procedure. In another preferred embodiment, wood flour also is combined with the microspheres when that ingredient is premixed with liquid resin in a plow type mixer before combination with the wood flakes, in order to reduce fluidization during blending of the resin and microspheres.

Problems solved by technology

In comparing various attributes of OSB with plywood, one of the OSB drawbacks in term of applications is that the weight of current commercial OSB is often about 10-20% heavier than that of similarly-dimensioned panels of plywood.

However, in general, when the density of composite lignocellulosic materials is reduced, the mechanical properties also tend to be reduced simultaneously.

However, the use of specialty foaming binders in place of normally used consolidation resins can increase manufacturing cost and process and product quality control issues and complexity for board processing.

These voids can significantly impact the process control and ultimate mechanical properties of the final mat product.

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